<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
//        let sb1 = Symbol("sb");
//        let sb2 = Symbol("sb");
//        alert(sb1 === sb2);     //false

        let sb1 = Symbol.for("sb");     //创建一个Symbol值
//        let sb2 = Symbol.for("sb");     //查找"sb"的Symbol值，有则返回该Symbol值
//        alert(sb1 === sb2);       //true
//        alert(Symbol.keyFor(sb1));      //sb
//        alert(typeof sb1);      //symbol

    </script>
</head>
<body>

<button>点击</button>
<input type="file" />
</body>
</html>